Sound muting assembly for gas flow duct systems

ABSTRACT

A sound muting assembly comprising a bar extending longitudinally through a duct, and a series of longitudinally spaced, laterally projecting vane supports which are angularly spaced from each other to define a helical path twisting about the bar. In one embodiment, the supports hold a sound muting vane comprising two twisted rectangular sheets of sound absorbing material spiraling around the bar on opposite sides thereof, and in another, two such vanes, each comprising two sheets, are supported to spiral about the bar in angularly spaced relation.

SOUND MUTING ASSEMBLY FOR GAS FLOW DUCT SYSTEMS BACKGROUND OF THE INVENTION This invention relates to a sound muting assembly, and has particular reference to a new and improved helical vane type assembly for effectively muting sound in a gas flow duct system.

Various attempts have been made to provide an effective assembly for muting or reducing the sound produced by gas moving through duct systems such as the intake or exhaust ducts of air conditioning systems, blowers for furnaces, exhaust stacks, and the like. One such attempt which has met with some success has been toemploy a sound absorber arranged in a helical configuration within the ducts of the system.

Typically, however, absorbers of that type have been relatively ,expensive to manufacture and install, and have required specially designed duct sections, thus necessitating extensive modification of the duct system itself. Further, such absorbers must be custom made for the particular duct systems within which they are to be installed and cannot be readily assembled for rapid installation at the jobsite.

SUMMARY OF THE INVENTION The present invention provides a new and improved sound muting assembly employing a helical-vane sound absorber which can be quickly and easily assembled and installed in virtually any duct system without requiring substantial modification of the duct system itself, and which will effectively reduce the noise level of the duct system when in use. Further, the assembly is inexpensive to manufacture and can be provided in kit form for installation at the jobsite.

More specifically, the assembly comprises a sound absorbing vane supported in a twisted, helical configuration within a portion of the duct system by a plurality of longitudinally spaced and laterally projecting supports attached to a bar extending along the centerline of the duct. The degree of twist of the vane is determined by the supports, which are arranged with each angularly spaced from adjacent supports to define a helical path around the bar.

In one embodiment, the assembly has a single vane which extends completely across the duct and is formed by two twisted rectangular sheets of sound absorbing material frictionally held on opposite sides of the bar by pairs of rods forming the laterally projecting supports. In an alternative embodiment, the apparatus has two such vanes arranged in longitudinally intersecting relation to divide the duct, in cross-section, into four equal sections.

The many features and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.

DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view, partly in cut-away crosssection, of a duct corner section within which is mounted an assembly in accordance with the invention and including a helical vane on a plurality of supports mounted on a bar which extends along the centerline of the duct;

FIG. 2 is an isolated perspective view of the assembly of FIG. 1;

FIG. 3 is a cross-sectional view of the vane, supports and bar of FIG. 2, taken substantially along line 3-3 of FIG. 2;

FIG. 4 is an isolated and fragmentary perspective view, partly in cross-section and phantom line, of one of the supports of FIG. 2 secured in position on the bar before assembly of the vane;

FIG. 5 is a fragmentary cross-sectional view of an edge strip clipped over one end of the vane of FIG. 1 and taken substantially along line 5-5 of FIG. 1;

FIG. 6 is a perspective view, partly in cut-away crosssection of a second embodiment of the invention employing multiple vanes and mounted in a straight-sided tubular duct;

FIG. 7 is an isolated perspective view of the supports and bar of FIG. 6 before assembly of the vanes;

FIG. 8 is an exploded perspective view illustrating the manner in which one set of supports for each of the vanes of FIG. 6 is assembled on the bar; and

FIG. 9 is a fragmentary cross-sectional view of the edge strip of FIG. 6 and taken substantially along line 9-9 of FIG. 6.

DETAILED DESCRIPTION As shown in the exemplary drawings, the present invention is embodied in a new and improved sound muting assembly 10 for use in gas flow duct systems, typically where air is the gas moving through the duct. In the embodiment illustrated in FIGS. 1 through 5, the assembly 10 is positioned in tubular duct 12 of circular cross-section having a longitudinal bend to form an elbow or comer section of a larger duct system, such a section typically having straight duct sections (not shown) attached at each end.

To mute the sound produced by gas moving through the duct 12, the assembly 10 has a sound absorbing vane 14 which preferably extends fully across the duct to divide the flow passage into two longitudinal portions. The vane 14 is formed as a helix and forces the gas to spiral as it moves through the duct 12.

In accordance with an important aspect of the invention, the vane 14 is a generally rectangular strip twisted into a helix by a plurality of longitudinally spaced and laterally projecting supports 16 attached to a bar 18 extending along the centerline of the duct. The supports 16 are angularly spaced around the bar 18 to define a helical path, and the vane 14 is attached to the supports to project outwardly from the bar 18 and twist therearound along the helical path. While a single sheet might be sufficient, with one edge extending along the bar and the other edge spiraling around the bar, the vane preferably comprises at least two such sheets disposed on opposite sides of the bar and each spiraling about the bar, the vane thus being a composite sheet which is, in effect, twisted about a longitudinal axis defined by the bar.

By virtue of this construction, the assembly 10 can be quickly and easily installed in virtually any portion of a gas fiow duct system to effectively reduce the level of noise of the system wherever necessary. Further, the apparatus 10 is economical to make and install, and can be provided in kit form for use in an existing duct system to substantially reduce the noise level without requiring new or additional duct sections.

As shown in FIGS. 1 and 2, the vane 14 herein is formed by two rectangular sheets of suitable sound absorbing material, such as expanded cellular plastic, extending along opposite sides of the bar 18 and each having a width substantially equal to a radius of the duct 12, less half a thickness of the bar 18. For the corner section of the duct shown, the bar 18 is longitudinally curved to follow the curved centerline of the duct 12 through the corner section. When the vane 14 is assembled, it extends diametrically (in cross-section) across the duct with the bar lying on the centerline of the duct.

The degree of twist of the vane 14 is determined by the angular positions of the supports 16 about the bar 18, which has a circular cross-section in FIGS. 1 through 4. Herein, each of the supports 16 comprises two identical rods 24 of circular cross-section arranged in spaced parallel pairs straddling the bar 18, each rod having a length slightly less than the diameter of the duct 12. Each of the rods 24 of a pair is secured to the bar 18 to project tangentially in opposite directions from one side of the bar so that the rods of a pair are parallel with each other and lie in a common plane perpendicular to the axis of the bar. Each rod 24 is attached to the bar 18 adjacent its mid-point so that the opposite end portions of the rod project equal distances outwardly from the bar (see FIG. 4).

To secure the rods 12 of each support 16 to the bar 18, a tubular collar 26 is telescoped over the bar and has two laterally directed cylindrical sleeves 28 attached at diametrically opposed points. The sleeves 28 are bored or otherwise formed to have openings therethrough with diameters substantially equal to the outer diameters of the rods 24 so that the rods can be inserted in the sleeves with tight friction fit. Herein, the sleeves 28 are welded to the collar 26 and the collar is secured in position around the bar 18 by sliding the collar over the rod to the desired position and then forming a dimple in the collar with a hammer and punch.

The vane 14 is assembled by sliding each sheet 20 edgewise into the space between the rods 24 of each support 16 until one edge abuts the bar 18. The spacing between the rods 24 of a pair is less than the thickness of each sheet 20 so that when the sheets are in position, the rods compress the sheets in the area of contact to frictionally hold the vane 14 in place. Herein, the rods 24 are shown to be straight and more closely spaced than the thickness of the sheets along their full length, although it will be apparent that the rods can be spaced farther apart at the bar 18 and bent toward each other near the sleeves 28 so that the spacing between rods of a pair is less than the thickness of the sheets 20.

As shown in FIGS. 1 and 5, the ends of the vane 14 are streamlined by providing edge strips 30 to cover the leading and tailing edges of the sheets 20. In this instance, the strips 30 are elongated metal clips having generally U-shaped cross-sections, and are frictionally attached to the ends of the vane 14. Preferably, the sides 32 of the strips 30 have internal grooves 34 which will seat over the rods 24 of the first and last supports 16, and are held in place by being clipped over the edges of the sheets, compressing the edges of the sheets between the sides of the strip as shown in FIG. 5.

When the vane 14 and strips 30 have been assembled, the assembly 10 is then inserted into the duct 12 by sliding it longitudinally into the selected duct section. Typically, the assembly 10 will be held in place within the duct 12 by welding, bonding, or otherwise attaching the strips 30 to the inside sidewall of the duct. In some instances, however, particularly where the gas flow will be of very low speed, it may not be necessary to secure theassembly l0 positively to the duct 12 since outer edges of the vane 14 may engage the inside of the duct with sufficient frictional resistance to prevent displacement of the assembly.

As previously mentioned, the assembly 10 is particularly advantageous since it can be provided as an inexpensive kit for muting sound in an existing duct system. In many instances, it may be necessary to install the assembly 10 in only selected portions of the duct system. For example, if the assembly 10 is to be used in the airconditioning system of an office building, it may only be required that the noise of the system be muted in the areas of air intakes or outlets since the noise in other portions of the system may not bev heard by occupants of the building.

Typically, the purchaser or installer can install the assembly 10 in such a manner that it will most effectively reduce the noise for the particular system in which it is used, regardless of the type of system. If the noise is relatively high in frequency, the installer can position the collar 26 and rods 24 of the supports 16 to define a sharp twist in a given length'of duct section. On the other hand, if the noise is of relatively low frequency, the degree of twist of the vane 14 should be less to more effectively absorb the sound and the installer can position the supports 16 to define less twist of the helical path for the same length of duct.

The length of the bar 18, spacing between supports 16, and the size of the vane 14 are determined by the particular duct section or sections within which the assembly 10 is to be installed. When supplied in kit form, the assembly 10 can be quickly adapted for a particular duct section by cutting the rods 24 of the supports 16 to a length slightly less than the length of the duct diameter, trimming the sheets 20 of the vane 14 to have a width approximately equal to the radius of the duct, and cutting the bar 18 to the length of the duct section to be muted. If necessary, as in FIG. 1, the bar 18 is then bent to follow the centerline of the duct section.

The number of supports 16 and their spacing are determined by the length of the bar 18, and the collars 26 are spaced to provide sufficient rigidity to prevent the sheets 20 of the vane 14 from sagging and to hold them along the helical path. Once the various components of the assembly 10 have been trimmed to the proper size, the installer then assembles the parts as previously described.

In some instances, particularly where the gas flow through the duct system is of relatively high speed and the pressure drop through the system is critical, the degree of twist of the vane 14 may be required to be less than that which would most effectively absorb the particular frequency of noise in the system since a greater degree of twist could produce a large pressure drop. In such situations, it may be necessary to use less twist in a given length and to provide more than one vane 14 for effectively muting the sound.

FIGS. 6 through 9 illustrate an alternative embodiment of the invention employing multiple vanes, and

components of this embodiment which have corresponding components to those of the embodiment of FIGS. 1 through 5 have been designated with corresponding primed reference numerals. In the embodiment of FIGS. 6 through 9, the assembly 10' has been shown in a straight cylindrical duct 12' and with two vanes longitudinally intersecting 14' disposed at right angles to each other and dividing the flow path through the duct into four portions.

As best seen in FIGS. 7 and 8, the bar 18 in this instance has a rectangular cross-section and the collars 26' similarly have a hollow rectangular shape. To position the supports 16' so that they define a helical path, the bar 18' is twisted along its length, the amount of twist being formed to correspond with the desired twist of the vanes 14.

Any suitable means may be employed to twist the bar 18', one approach being to secure one end of the bar in a vice and then apply torque to the opposite end with a hand-held wrench (not shown). After the bar 18' has been twisted, the collars 26' of the supports 16' are slipped over the end of the bar, the sleeves 28' in this instance being welded to opposite sides of the collars, until each collar is in the desired position along the bar.

To support two vanes 14' at right angles to each other, the collars 26' are arranged in pairs with the rods 24' of one collar of a pair projecting laterally in angularly spaced relation with the rods of the other collar. This is accomplished by orienting identical collars 26' so that the rods 24' of one collar are disposed at right angles to the other before the collars are slipped over the end of the bar 18', as shown in FIG. 8.

The two vanes 14' are then assembled on the supports 16' by slipping each of the sheets 20', herein four altogether, between the pairs of rods 24' along the respective helical path defined by the rods of the supports. In this manner, each sheet 20' .is angularly spaced 90 from the adjacent sheets and the four sheets form two vanes 14' extending diametrically across the duct 12' at right angles to each other, each spiraling in spaced relation with the other about the bar 18'.

In FIGS. 6 and 9 is shown an alternative form of edge strip 30 for the ends of the vanes 14, this edge strip having particular utility in a high speed flow situation. Each edge strip 30' has a pointed base 36 for smoothly diverting the gas flow as it enters the area of the assembly l and herein comprises two integrally formed clips intersecting at their midpoints in the form of a cross (see FIG. 6). Each edge strip 30' is clipped onto the ends of the vanes 14' and overlies the end of the bar 18' as well as the end portions of the sheets 20' of the vanes.

From the foregoing, it should be apparent that while the embodiment of FIGS. 1 through illustrates only a single vane 14, additional vanes can readily be provided if necessary. Similarly, additional vanes 14' can be added to the embodiment of FIGS. 6 through 9 simply by adding a third support 16 to each pair of supports and preferably changing the cross-section of the bar 18' to hexagonal rather than square as shown.

The diameter and configuration of the duct section within which the assembly is to be used may be of virtually any size or shape. If necessary, several individual duct sections with assemblies therein can be connected together to form, essentially, one continuous sound muting assembly.

While difi'erent specific forms of the invention have I been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention.

I claim:

1. A sound muting assembly for use in gas flow duct systems, said assembly comprising:

an elongated bar;

a plurality of laterally projecting supports longitudinally spaced along said bar, each of said supports being angularly spaced from adjacent supports to define a helical path about said bar;

and an elongated sound absorbing vane extending along said path and twisted helically around said bar, said vane being held by said supports on said path.

2. A sound muting assembly as defined in claim 1 in which each of said supports comprises a pair of parallel rods of preselected length secured to opposite sides of said bar and projecting laterally therefrom, and said vane being held by each support between the rods thereof.

3. A sound muting assembly as defined in claim 1 in which said vane comprises two sheets of sound absorbing material arranged on opposite sides of said bar and forming a single vane twisting helically about said bar.

4. A sound muting assembly as defined in claim 1 in which said vane comprises two sheets of sound absorbing material and each of said supports comprises a pair of parallel rods of predetermined length secured to opposite sides of said bar and projecting laterally from opposite sides of said bar, said sheets each being held between the rods of a pair thereby to be supported along the helical path.

5. A sound muting assembly as defined in claim 4 in which said bar has a circular cross-section and said rods are attached to said bar by a pair of sleeves secured to opposite sides of a hollow cylindrical collar telescoped over said bar.

6. A sound muting assembly as defined in claim 5 wherein edge strips are mounted over the ends of said sheets to streamline the leading and trailing edges of said assembly.

7. A sound muting assembly as defined in claim 4 in which said bar has a rectangular cross-section and is twisted along its length; and said rods are attached to said bar by a pair of sleeves secured to opposite sides of a hollow collar having a rectangular cross-section and telescoped over said bar.

8. A sound absorbing assembly as defined in claim 1 wherein multiple sound absorbing vanes are twisted helically about and supported on said bar in angularly spaced relation with each other.

9. In combination with a hollow and generally cylindrical gas flow duct, a sound muting assembly comprising:

a bar extending along the centerline of said duct;

a plurality of supports projecting laterally from said bar and spaced longitudinally therealong, successive said supports being angularly spaced from adjacent supports to define a helical path about said bar;

and a sound absorbing vane twisted about said bar and mounted on said supports to lie along said helical path.

10. The combination as defined in claim 9 in which said vaneextends diametrically across said duct and each of said supports comprises a pair of parallel rods arranged on opposite sides of said bar in a plane normal to the length of said bar.

11. The combination as defined in claim 10 in which said rods are attached to said bar adjacent their midpoints and the ends of each rod are spaced equal distances beyond said bar; and said vane comprises two twisted sheets of sound absorbing material extending along opposite sides of said bar and supported between said pairs of rods.

12. The combination as defined in claim 11 in which said bar has a circular cross-section and said rods of a pair are attached to said bar by a pair of hollow sleeves secured to opposite sides of a hollow cylindrical collar telescoped over said bar.

13. The combination as defined in claim 11 in which said bar has a rectangular cross-section and is twisted along its length; and said rods of a pair are attached to said bar by a pair of hollow sleeves secured to opposite sides of a hollow collar having a rectangular cross-section and telescoped over said bar.

14. The combination as defined in claim 11 wherein flow-streamlining edge strips are positioned over the leading and trailing edges of said vane.

l K I i l 

1. A sound muting assembly for use in gas flow duct systems, said assembly comprising: an elongated bar; a plurality of laterally projecting supports longitudinally spaced along said bar, each of said supports being angularly spaced from adjacent supports to define a helical path about said bar; and an elongated sound absorbing vane extending along said path and twisted helically around said bar, said vane being held by said supports on said path.
 2. A sound muting assembly as defined in claim 1 in which each of said supports comprises a pair of parallel rods of preselected length secured to opposite sides of said bar and projecting laterally therefrom, and said vane being held by each support between the rods thereof.
 3. A sound muting assembly as defined in claim 1 in which said vane comprises two sheets of sound absorbing material arranged on opposite sides of said bar and forming a single vane twisting helically about said bar.
 4. A sound muting assembly as defined in claim 1 in which said vane comprises two sheets of sound absorbing material and each of said supports comprises a pair of parallel rods of predetermined length secured to opposite sides of said bar and projecting laterally from opposite sides of said bar, said sheets each being held between the rods of a pair thereby to be supported along the helical path.
 5. A sound muting assembly as defined in claim 4 in which said bar has a circular cross-section and said rods are attached to said bar by a pair of sleeves secured to opposite sides of a hollow cylindrical collar telescoped over said bar.
 6. A sound muting assembly as defined in claim 5 wherein edge strips are mounted over the ends of said sheets to streamline the leading and trailing edges of said assembly.
 7. A sound Muting assembly as defined in claim 4 in which said bar has a rectangular cross-section and is twisted along its length; and said rods are attached to said bar by a pair of sleeves secured to opposite sides of a hollow collar having a rectangular cross-section and telescoped over said bar.
 8. A sound absorbing assembly as defined in claim 1 wherein multiple sound absorbing vanes are twisted helically about and supported on said bar in angularly spaced relation with each other.
 9. In combination with a hollow and generally cylindrical gas flow duct, a sound muting assembly comprising: a bar extending along the centerline of said duct; a plurality of supports projecting laterally from said bar and spaced longitudinally therealong, successive said supports being angularly spaced from adjacent supports to define a helical path about said bar; and a sound absorbing vane twisted about said bar and mounted on said supports to lie along said helical path.
 10. The combination as defined in claim 9 in which said vane extends diametrically across said duct and each of said supports comprises a pair of parallel rods arranged on opposite sides of said bar in a plane normal to the length of said bar.
 11. The combination as defined in claim 10 in which said rods are attached to said bar adjacent their mid-points and the ends of each rod are spaced equal distances beyond said bar; and said vane comprises two twisted sheets of sound absorbing material extending along opposite sides of said bar and supported between said pairs of rods.
 12. The combination as defined in claim 11 in which said bar has a circular cross-section and said rods of a pair are attached to said bar by a pair of hollow sleeves secured to opposite sides of a hollow cylindrical collar telescoped over said bar.
 13. The combination as defined in claim 11 in which said bar has a rectangular cross-section and is twisted along its length; and said rods of a pair are attached to said bar by a pair of hollow sleeves secured to opposite sides of a hollow collar having a rectangular cross-section and telescoped over said bar.
 14. The combination as defined in claim 11 wherein flow-streamlining edge strips are positioned over the leading and trailing edges of said vane. 